The present invention relates generally to infusion systems and methods, and more particularly, to a system and a method for controlling the self-administration of analgesics to a patient while monitoring a physiological parameter of the patient.
Programmable infusion systems are commonly used in the medical field to deliver a wide range of drugs and fluids to patients in a variety of settings. For example, syringe pumps, large volume pumps (herein referred to as “LVP”), and flow controllers are used in hospitals, clinics, and other clinical settings to deliver medical fluids such as parenteral fluids, antibiotics, chemotherapy agents, anesthetics, analgesics, sedatives, or other drugs. Single or multichannel systems are available, and different systems have various levels of sophistication, including automatic drug calculators, drug libraries, and complex delivery protocols.
Still other types of drug delivery systems include a patient-controlled analgesia (herein “PCA”) pump and a patient-controlled epidural analgesia (herein “PCEA”) pump. With a PCA pump or PCEA pump, the patient controls the administration of the narcotic analgesics since the patient is usually in the best position to determine the need for pain control. PCA is commonly administered via a stand-alone infusion device dedicated solely for PCA use, such as a syringe pump having the required programming and patient request button or switch. Typically, the patient holds a button switch in his or her hand. The request button is wired or wirelessly connected to a PCA pump or separate controller that controls the PCA pump. When the patient presses the request button, the PCA pump or controller provides the patient with a programmed dose of analgesia or other medication. A PCA protocol program is contained in the PCA pump or separate controller and processes the patient request against various factors to determine if the analgesia requested by the patient should be administered.
Regardless of the type of pump system used, an undesirable side effect of the administration of drugs, particularly anesthetics, analgesics, or sedatives, can be central nervous system and respiratory depression. The ability to avoid overdosing such drugs is an important concern. While improvements have been developed in infusion systems where sophisticated automatic programming and calculation features have been designed to minimize medication programming errors, it is possible for patients to experience respiratory depression or other deleterious effects during the administration of narcotic analgesics or sedatives during in-patient or out-patient clinical procedures. Even in PCA applications, where overdoses are typically prevented by the patient falling asleep and therefore being unable to actuate a delivery button, there have been cases of respiratory and central nervous system depression associated with the administration of PCA. The causes include clinical errors in programming the PCA device, errors in mixing or labeling analgesics, device malfunction, and even overzealous relatives who administer extra doses of analgesics by pressing the dose request cord for the patient.
Because of the potential for respiratory or central nervous system depression due to narcotic analgesic overdose, narcotic antagonists such as naloxone (Narcan™) are widely available and commonly used in hospitals for reversal of respiratory and central nervous system depression. However, the effectiveness of such narcotic antagonists is highly dependent on prompt recognition and treatment of respiratory and central nervous system depression. Therefore, it would be desirable to monitor the actual physical condition of the patient to find respiratory or nervous system depression so that immediate remedial measures may be taken.
For the detection of potential respiratory depression associated with the administration of narcotic analgesics, sedatives, or anesthetics, a system that indicates a patient's respiratory status and cardiac status without the need to invasively measure or sample the patient's blood is particularly desirable and useful. Non-invasive end tidal carbon dioxide (“EtCO2”) and pulse oximetry (“SpO2”) monitoring are two technologies used to monitor physiological parameters of a patient. The EtCO2 method monitors the concentration of exhaled and inhaled CO2, respiration rate, and apnea (respiration rate of zero) while pulse oximetry monitors the oxygen saturation of a patient's blood and the patient's pulse rate. The combination of EtCO2 concentration, respiratory rate, and apnea or the combination of the blood oxygen saturation and pulse rate can be important indicators of overall patient respiratory and cardiac status.
One common approach to non-invasive pulse oximetry uses a dual-wavelength sensor placed across a section of venous tissue such as a patient's digit to measure the percentage of hemoglobin oxygenated in the arterial blood, and thereby estimates the patient's oxygen saturation level. In addition, since the oxygenated hemoglobin at a specific tissue position is pulsatile in nature and synchronous with the overall circulatory system, the system indirectly measures the patient's pulse rate. Examples of similar pulse-oximetry sensors are disclosed in U.S. Pat. No. 5,437,275 to Amundsen et al. and U.S. Pat. No. 5,431,159 to Baker et al., incorporated herein by reference.
Another means of monitoring the respiratory status of a patient is by measuring and charting EtCO2, a procedure known as capnography. In particular, current capnography devices utilize spectroscopy, for example infrared, mass, Raman, or photo-acoustic spectroscopy, to measure the concentration of CO2 in air flowing through a non-invasive nose and/or mouthpiece fitted to the patient (for example, see U.S. Pat. No. 6,379,312 to O'Toole). Capnographic EtCO2 waveforms and indices such as end tidal CO2 concentration, or the concentration of CO2 just prior to inhaling (also referred to as fractional concentration of carbon dioxide in inspired gas or “FICO2”) are currently used to monitor the status of patients in operating rooms and intensive care settings.
Patient care systems providing for central control of multiple pump modules, including PCA modules, are known in the medical field. Such a care system generally provides a controller which interfaces with a plurality of individual pumps to provide various control functions. An improved patient care system of this nature is disclosed in U.S. Pat. No. 5,713,856 to Eggers et al., incorporated herein by reference. The central management unit of the Eggers et al. system can, for example, obtain infusion parameters for a particular infusion module from the clinician and serve as an interface to establish the infusion rate and control the infusion by that infusion module accordingly. It can individually control the internal setup and programming of each functional module, and receive and display information from each functional module. The Eggers et al. patient care system also provides for the central control of various monitoring apparatus, such as pulse oximeters and carbon dioxide monitors.
In more advanced systems that have provided substantial benefit to the art, control over a PCA system is provided in conjunction with monitoring a patient's physiological parameter or parameters. In the case of U.S. Pat. No. 5,957,885 to Bollish, a pulse oximetry system is disclosed and in the case of U.S. Application Pub. No. 2003/0106553 to Vanderveen, a EtCO2 system is provided. Both of these systems have provided a substantial improvement in the art. Improvements to those and other systems have been provided by U.S. Application Pub. No. 2005/0177096 to Bollish, Brook, and Steinhauer, incorporated herein by reference. Improvements include providing a trend of respiration or pulse rate with the dosing of the analgesic superimposed so that a trend of the patient's physiological parameter and response can be seen clearly and rapidly. Additionally, improvements include expanding a drug library to specifically include various PCA dosing parameter limits.
Furthermore, the system in accordance with the above provides automatic inhibition of patient-requested medication (referred to hereafter as “pausing”) of the PCA module in the event of respiratory depression. Without automatic PCA pausing, continued administration of the narcotic analgesics may aggravate respiratory depression until appropriate medical personnel arrive to intervene. The time it takes for medical personnel to recognize a problem and intervene will delay administration of narcotic antagonists and thereby potentially compromise their effectiveness.
Improvements to PCA systems in which patient physiological data is considered in real time permit further benefit from the PCA system. Patients can receive treatment while an automatic PCA shut-off or “pausing” feature lessens the risk of inadvertent respiratory depression. However, it has been noted that unwanted pausing of PCA infusions can occur due to false alarms. Under the programming of at least one system, a PCA system that has been automatically paused cannot be restarted without manual reset of the system by a clinician. During this “paused” period, the patient is unable to receive analgesia or other treatment desired.
False alarms are typically caused by transient, short term physiological and electrical artifacts in monitored data. False alarms are undesirable because they result in the PCA system pausing inappropriately depriving the patient of needed pain medication. They also place additional burden on caregivers to investigate the event and re-activate the system.
Hence, those skilled in the art have recognized a need for an improved patient care system and method that can monitor the physical condition of a patient and can control the infusion of PCA or PCEA to the patient based on the analysis. Further, those skilled in the art have recognized a need for an improved patient care system and method that can not only automatically pause a PCA or PCEA system, but also lessen the risk of false pausing episodes. The present invention fulfills these needs and others.